Remote line concentrator



Feb. 16, 1960 P. M. LUcAs more Lm;r coNcx-:Nm'ron Filed oct. 4, 1957 7 Sheets-Sheet k1 PIERRE M- LUCAS VERE@ @L EEU,\.

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Feb. 16, 1960 P, M, LUCAS 2,925,473

' REMOTE LINE coNcEN'rRE'roE y MEAN, MJA

Feb. 16, 1960 P, M, LUCAS 2,925,473

'REMOTE LINE CONCENTRATOR y I Filed 0st. 4, 1957 7 Sheets-Sheet 3 PIERRE M. LUCAS INVENTOR @LJ/Laux@ Feb. 16, 1960 l' P. M. LucAs 2,925,473

` REMOTE LINE CONCENTRATOR Filed oct. 4, 195? f 7 sheets-sheet 4 PIERRE M. LUCAS INVENTOR MMM M Feb.vl6, 1960 P. M. LucAs 2,925,473.

REMOTE LINE coNcENTRAToR Fiied oet. 4, 1957 '1 sheets-sheet 5 PlERRE M. LUCAS INVE NTOR Feb. 16, .1960 P. M. LucAs 2,925,473

REMOTE LINE coNcENTRA'roR '7 Sheets-Shea?l 6 Filed oct. 4, 1957 al I j PIE R RE M LUCAS INVENTO Feb.16,196o P. M, LUCAS 2,925,473

' `'REMOTE LINE coNcENTgA'roR Filed oct. 4, 1957 7 sheets-sheet v PIERRE-M, LUCAS INVENTOR MJJGJ This concentrator or concentratingl switch UnitffdV States i F 925,473." nnMo'r'nLnsncoNcNrnATjoR P ierreMtLucas,'Issy-les-Molineaux, France; l' application.0cberf4r1957SriatNQ. 6.818.196.

-(laililspriority, application' France-October 5,119.56 1 Y whims@ The' :present invention relates to` aeftelephonic concen trator allowing a numberV of` telephoner "subscribersto be connected to: acentralfsta'tiomby a-smallernumber of trunkzlines,` and particularly tog an electronic switching network ima central office.v f

mayl be locatedintheffsame building asthe central orice .but'it' is preferablyl'ocated remote from' the central office adjacent the`-subscribers andfadvantageously inthevicinityof the numberJ of fsubscribers.

certain number of subscribersto-bel connected to -a centhe"numbenoffsubscribers, but; in these systems-at the point lofarrival o f` the trunk Vlines at the centralo'ce,

there \isj`r adeconeentration which-'leads to individual callingandldisconnecting relays thatare equal in number to the subscribers, so that,y for the central oi'ice, the sub-- scribers connected to the"concentrator arev not distinguished from the normal Subscribers, the only condition to'be complied with being a condition of synchronism in the operation of` the concentrator and of the deconcen'- traton Anobjectof the present'inventionis to construct'an electronicy concentrator which canbe connected to van entirely electronic central station.V`

A'Another''Object ofthexinventinis to use directly, inr thecentralY oice, the information conveyed'byahum- Herfof'concentrator trunk linesless than thefnumbe'r tilted-by thegtwoswire circuits. the function ofrfj whi s to transmit'the s ynchfronising rpulsesandj'the s ignall g Petentd. Feb 1.6 1,9550A the establishment lof/communications "tov use, fo1f,1 :l 1 e jr transmission" of information from the central; fice to the concentrator switching stage, the samejconentrator trunks'aridein addition, a very-limited'number .oftw'oy Wire cuitsa'the. funsfio'n ofwhisli isltgirasfnifrespe! C'i-lly Ynhonisingrulses andrfsignallmaffsquencles A other object oftheinvention is' to vprovide a concen.

trator which `is wi t hout any source of direct or alteriggitfY vin? vsuplilyglffhef energy, necessary for itSOP-eratign. being ircuit co kfermate v.feed on a phant obtained byy frequencies?, 'gAnQther Obie@ 1liA c 'en'tralb the signallinggf aallins Subscribers-,lille Qf ihetmvenion is n. anni n th tratar man avalable'tunlsline; this eliminatesthe neces- Y matrigna une TheI ariirciple" of 'the c olicentrator. willy 4be Hereinafter.. the; details. of the operation' of; .the el "i lllslltfrleWill.notbedescrbedsfitpwillbe= *y etica Y "sieht widesgribfbtlefly the Vprinci les of lits const and'v i V"d est conetgn' withl the 'concentrater-- sity' fgsearchnaforithe Calliagfline andLof dem g munication.

Another Object 0f the inventionris t0 eiest the @0nneotion, tojthe exchange, of' a called subscribers line. by transmitting,l on a selected" concentratortrunk, a conf nesting Puls'eat a timeinterval xed within the recurrent hejnfsmbers which., are brought info. 0Peratin, ih

rewi1j1,.-be taken. as a -r'10 r11 i 111'it,1ive; examplna central' station whichan', serve live thousandrsubsc'ribfers supposed. 1to' 'be distributediovera hundred concentrahtor sA at the frate of vfifty Subscribers per Ceueutratgr, each C011- .centrator being connected tothe electronic; ceritraIISta;y tionj by ten'trunk lines; this, makes a total] of -a thousand trunl` lines .leadingjto the. centralf station.

lItV wiljlf also b e assumed, in orderto x ones ideas, that` the' connection elements' o ffthe central station are disf tributed li r 1 rectangular switchboards in accordance with a structure similar to vthat of thecrossbar systems with, for

example, six selection stages in cascade distributed in -two grups'fof thr ee stage s, theiirst group of'these selection stages, called incoming line Y link, which enablesfevery one ofthe;thouseurd` incoming trunk lines tofbe connected`- `to any one of eight hundred or athousand intermediate members hereinafterafor the sake of simplicity, dentd by theterrn junctor, and the second group ofv three of subscriber'linesfWithoutgitjbeing necessary 4to use a` Another object'. of thexinvention isfto use, forl transmitting--to the central stationythefsignals containing the information relating to'fthe stateof allthe subscribers f linesponnected to the cono'entrator,a-sequentialdivision` code infthetime'suchthat a -xedetimeginterval in' a recurrent -cycle fis characteristicY of afsingle'fsbscriber;

"f Theremote linel concentratorvo f the invention" belongs v "tofth'e kind oconcentrators@employing a rectangular -switching arrangement of fcrossploint'shaving 'a number ofsubscriber-'line inputs inone'cogordinate' and ajnumber of trunk inputs in the otherA co-ordinate. The cross-l points are gas tubes that'pass either talking alternating current signals or direct current signals'derived fromthe Yfeeding'voltage of the subscribers handsets.

Another object of the invention is to utilizegfor the transmission of information YrelatingA to the subscribers line servicecondition towards vthe switching network of 'lelemnS-Q l arelcapable'of,assuming'two well deneclI physical states,

f fandifrequencie's' of up to about'20kilo'cycles per second i's pfossiblewithout any appreciable attenuation and .the

lselectionstages, called outgoing line link, whichenfA `ablesanyo1 1` e of 'these junctorsrv to be connected to` any Qnegf the theusandoutgoing trunk lines l Y Without preiufilgingthe physical nature .0f th Cr- QSSz points` QIering'the constitution of these selectionstages that are. lnsidethecent'ral office, it will beass'umed onlyk fha't'fit is" possiblejftg Produce', an end-Ieren@connection markingpot' tialsontotlie incoming trunkfline, thev outgoing 4trn'ik line selected by. any s 'uit,,v Y

It; will; alsobe supposed that the cro'ssfpoints whih' the tr ansmissi on of the audiotrequencies Ai other inwhicheverytransmission is considera-bly attentith Central Oce, lnly; thetrunkline's which serve for Afor example, fa hundred milliseconds. lThis recurrent cycle (Fig. '1, line a),V is dividedfin fifty maiorcyclesii eah having. a'duration, 0f tw mi! seconds andbeingr respectively characteristic vof the su Y 3 scribers No. 00, No. 01, No. 02 No. 49 of the hundred concentrators. Each of the fifty major cycles is, in turn, divided into a hundred minor cycles, each having a duration of twenty microseconds and being respec-v tively Vcharacteristic ofthe first, second, etc. hundredth' concentrator. Y

Consequently, a minor cycle constitutes a timeinterval which is characteristic of a particular subscriber of the exchange, theV number of this minor Vcycle fixing the concentrator and the number of the major cycle to which it belongs fixing the number of the subscriber in the concentrator'to which heis connected. Thus, there will be allotted to the subscriber No. 02 of the concentrator No. 5, in theconcentraton the time interval constituted by the third major cycle and, in the electronic central office, the time'interval constituted by the fifth minor cycle of this third major cycle. v

This division of the time into major cycles renders it possible to keep a rather coarse time division in the concentrating-switch stage and does not necessitate the employment of pulses of very short duration Within said stage, the fine time division being transferred into the electronic central office itself, the circuits of which can be more easily supervised.

Thelconcentrator comprises essentially a rectangular switching arrangement or matrix which'will hereinafter be assumed' to be of the Vsame nature as those ofthe selecting stages of the central switching network, a pulse generator synchronized to the operating rate of the central office switching network and generating subscriberidentiiication pulses at suitable time-positions over .a total of fifty members which will be called -gates, each being allotted to a particular subscriber of the concentrator.k The function of these gates consists essentially in .allowing to pass or in blocking signalling pulses and frequencies, according to the service condition of the subscriber line andvaccording to the state of the crosspointswhich have been allotted to said line in the'concentrator.

` When a subset is off-hook, the microphone feed current, which hows in the line,` modifies the characteristics of the gate relative to this subset, so that pulses of great amplitude derived from the subscriber-identifying pulsesV y supplied by the pulse generator can be propagated to the connecting rectangular matrix.

The effect of these pulses of high amplitude, which will hereinafter be called one-sided connecting pulses, is to allow one of the crosspoints associated with 1 the subscriber line to be operated,.that is to say to obtain a path of negligible attenuation between the line of the subscriber and one of the trunk lines going to the centraloce switching network.

The operation of the crosspoint produces a double action: it again modifies the characteristics of the subscriber gate in such a manner that all the signallings in the direction of the central office are blocked and, on the other hand, it produces on the corresponding trunk line the transmission, to the central office, of a -pulse which will hereinafter be called connection control pulse and which enables the central oice,'by analysis of the time interval kof this pulse, to know the number of the subscribers line which has just been connected into the con-V centrator and to connect the trunk line, which has j ust been engaged, to a sender device. The trunk-line circuit at the central oice then transmits a dial-tone signal to the subscriber for the purpose of inviting him to dial his number. Y

During dialling, breakdowns of thesubscriber loop occur; the interruption of the microphone feed current produces, in cadence, modification of the characteristics of hisrgate which are' such that, during the period of the breakdowns of the loop, a special frequency ,signal called loop frequency is transmitted through the connecting rectangular matrix andto the selected trunk line inthe direction ofthe central oflice. This loop-frequency signal, when detected by the trunk-line equipment, enables the central oce to register the number of subscriber.

When the subscriber replaces his handset at the end of the communication, the same signal at the loop frequency is transmitted and analyzed in the same manner by the central office. After a certain interval, the central ofce,

the called recognizing that there has been a replacement of the l handset, releases the connection as will be seen hereinafter.

Y When the central office has received a number of digits that are sufficient for making the connection between the incoming trunk line and an outgoing trunk line, it proceeds to make this connection by operations which will not be described herein. The calling subscriber can hear all the tones which inform him of the result of hisrcommunication, e.g. an audible ringing tone, a busy tone, automatic anouncers etc., and, finally can enter into conversation with his correspondentwhen the latter lifts his receiver. f Y Y A If the correspondent is the first to replace, his handset at the end of the communication, the calling subscriber hears` the busy tone which invites him to replace his receiver:

also.

time in the concentrator of the calling subscriber.

When the calling subscriberreplaces his handset, the loop-frequency signal passing through his gate Aand detected in the trunk-line equipment signals to the central office that it should proceed to the release of the line. One will not concern himself'herein with the manner in which thekcentral office releases theV internal selection stages which have-been' used for the communication but` only with disconnection of the concentrator.y To dothis,

the central office Ytransmits over the trunk line pulses of high amplitude called disconnecting pulses which,v produce the release of the crosspoint used in the concentrarv tor.

After the release, the characteristics of the subscribers;

gate have again been modified and the gate is anew ina waiting position which Will be called idle condition.

In this condition, the gate allows the passage, in the direc,

opposite polarity and coming from the central office, serve for effecting the connection of a particular subscriber line for the arriving communications.

. When the'central office desires to effect the connection,v to a particular called subscribers line, which isassumed'` to beidle, it produces on all the free trunk'plines the transmission of a y,two-sided connecting pulse which `is similar to that .supplied by the `gate of the calledsub scriberbut of opposite polarity. This pulse, beingrtrans-,

mitted in the Vtime interval which is characteristic Eof the called subscriber, fis therefore in synchronism with that l. which comes from the gate,

duces the operation of the crosspoint of the rectangulary matrix which is at the crossing point of one of the trunk lines and of the line of the called subscriber. As before, the operation of this crosspoint produces a double action; it produces on the corresponding trunk line the transmission, to the central cnice, of a connection con.

trol pulse which enables it to know the number of thev trunkline which has been selected and consequently, to,

No operation is produced during the whole'oflthis sion ofthe signalling frequencies;

comme proceed: tofth'eernaking` of? conuectionate theinternal n selectionistages-and,.onfthe: other hand" itapoduceszaf modificationof: the; characteristics; of; .thea subscriberst t line-Zitogthe gate 3fwhich: comprises'faf bdlk'tnce'd;lov;

` frequencyl transformer 4 and rtn/0^saturableecore;transe gate;` The.resultothisistozallovwthepassage;. tothe;

stoppagenof this" loop-.frequency signal?y isc subsequently detected r as characterizing. thetliftfin'gf of'a the rreceiverfiby'v the called subscriber. Y

Simultaneously5vthe trunk' equipmentfengvaged in he vcentral office transmits two' charac: stictsignallin'g-audio frequencies: onthe=-one'lian ,vtheJ iectin'ofth'e set of? aref causa Subscribete-nie ringing; ime :signer whichA e* produces the operationvof itsnacoustic ringing andfonstlie' otherhand,` in tliefdirection' oithetrunk equipment nected withthecanig Subsc-rib'er;.acontinuelle.ffequneyv called ringing supervisory-l-iequencyifof return ofcall,

the'function of which willi be to enableV the;trunk'equip- Inient ofthe-callers endto be informed through' thefiir-A ternalselection stages ofthejcentraloce; of thermo? ment at` which the called subscriber liftsehisfhandsetiand, consequently, to proceed'to all thefoprer'ationsfthat are useful at that moment; inparticularlto' the pricing-;pwhich operations will not be described'thereinf I This frequency will not be'used on the lines whichare-'not togive Vrise topricing. v

LAs the lifting offhishandset-by the ealieasubseribermodifies the'characteristics of his-gate in a direction such that all signalling is b1ocked,ethe stoppage ofv the-loopfrequency signal which results therefromis'int'erpreted by the trunk-line equipment which stops-the'transmis-r Other objectsand features'o'f the in reading the detailed descriptionwhicliwill nowb'e sbseriherfinf question is,-

02,.-ot-tt1naA cencentratorfNot 5. This subscribersisubsetzis.connectedb the-.two 'e formers 5 and .6; The supply of .microphone;current,;ofy the'subscriberzs subsetv is obtainedtfrom,'thegremoteffeedz phantomI circuit; `the terminals of which are; represented: at V`7; through resistors'8=and1 the primary: windingszoffgthet transfomnersz4`v andj 5.

cuitfor theaudiofrequencies.;v i v t e l,

'The rectangulary switching arrang'ement-10 comprises fifty 'incoming leads such asi-11f Vandlterrz Aoutgoing :leadsv suchals-$142,; At the crosspointl'y offtvvo',incomingrandoutwhichisfrepresentedinithe figure, V"altl'iou'g'h Athere arefivr hundred 1 for the; whole of `the rectangular switching-ff ra,k

lie-'constituted by--alfcold-cathodegas.tube,.fbut2itiis. ,quite i' .i i l obviouskthat the man skilled in the artcaun'k devise aLnun-iav y j ber of modifications -thatj utilize` other v*devicesn-having Y similarproperties; the saidmodificationsforlinglpartfof thescope-ottheTpresentjinvention Tlie outgoingleads)y l such-as- 12flead, toth'eprimary winding:loftransformer; j, 14; the secondary winding of which is connected `tov oneV v invention willap'pear' giyen of a particular` non-limitative embodiment'with the aid of the accompanying drawings, vin whichA Fig. lis a pulse diagram Whiclivflias'been eiqJlainedY partly hereinbefore, fr v, r

Fig. 2 represents rdiagrammaticallyrV the-concentrator connected with a single subscribersy 'line' andj a single trunk line,

Fig. 3 representsV a trunk-line'equipment at'the central tice represented diagrammatically; K

Fig. 4 represents the synchronized whichforms part of the concentrator, s l

Fig; 5 represents a scanningdevicev which formse'pa'rt of the common members ofthe centraloceandenables pulse generator the latter to obtainall` theinformation which 'enables' it, n

when a connection takes place in a concentrator, to identify, at the same time, the number ofthe subscribers line and the number of the'trunk lineconkcerned,Y

Fig. 6 represents another scanriing-deviceV Whichg enables wire susbcriberlines andyonfthevotlierhand, tol'th'efcen- -v f Vtral office by means oftentwor-wire trunl'lines: In

addition, two two-'Wire i' auxiliary circuits y al 4o] connect the'central ofce to the 'concentraton oneconveying syn;

chroniizng pulses and the othertheloop-f're'quency signaly e s coming from the central ottce Thephantom circuit formedibyfthese twoqauxiliraryf circuits is used forthe remote feeding;'witlif-"direjct cur.-

' throughVV a! load resistort6 through the intermediary/@pflonepofthe fifty outgoing leads, such as' .19;Po'fftliis generator. .j i

ofthe ten trunk lines-such :sas-V15 y'and are finally: connected remoteffeed Source:y 4 v Qnftheotherside; the ingoingfleads'- such as-llleadfto' thefseries connectedsecondary windings of the trans formers 4,1s5fand6, and are connectedfthrough aresistor` 1 7', to ,the positive pole offth'e yrernotesfeedTsource'.

9 Thelsaturablecore: transformers 5f andpos'sesssecs "ondary'vwindingsr which receive'i'n series, thesubscriber-y identifying pul'sesjncoming from" the pulse-generatori 18 'finV theI time int'c rval/"thatds"characteristic of f the'subscriber,

Two-'subsidiary two-wireiines izo* arida;y waneer me:

concentrator tojthe central*A office; The l,line 20conveysl the Vsignal "having thefloop' frequency f, which is produced bythe oscillatorjZ/l that is common to all the-concem V'trators that are'connected to the central oceswitching network. The lineZ-Z conveys the synchronizing pulses thatl are produced, by the pulse-generator Z3 which is likewise common to the whole central office! These .synchronizing pulses areftransrnitteduwith a: repetition frequency: 'of 5:00 c./s.; they vcoincide withv the'commencement of` each minor cycle which relatesv to the concentrator considered (pulses 101 of'Fig; 1*)bu't maybe timedisplacedf'in advance by a period which is,A equal to the l to-and-fr'o' propagation; of the pulses between; the centhe central oHce to know at any moment theservi'ce con-f soz rentgof the concentrator which isfassumedtolbe'tlocated at a certainv distance from" the principal centralo'ice,

l Referring to Fig. 2, I/dcnotes the concentrator and IAI` denotes the"centralplce.v 1f denotes one subscribersl subsetof'fty such subsets: It Will'- be` assumed" that the;

ldsssrisktV with reference 'f to the, description of .thatf ligure,

" ,A rectangle comprising.;jafinedial' Aline" ofsep s l represents ja" bistable trigger; thefrsfsehcsf numeralv oifj f (this jtrigger is Vwitten' in this 'upper half 0f-thtrstang1= `The trigger "Tis assumed to pass into the:correspn'ruling'` 'condition'V lien: a trigger-pulse arrives throughthe con- 11Ct01is-lssdngtt0 this upnerlhslf; theA triggfsrVK is then?` assuntedto actjuponthezoutgoing connections which are` tralotlceY and thev concentrator; The transformers*` 24, 25', 21S-arid` 27, whichmare placed ony the'subsidiarylines` '2`0fand 22, are'` usedior constituting the remote,l feed phantomcircu'it between the battery^2 locatedjat rthe central oi'ce II and they terminals @usedyinthe' cony 1 Y' ventions' will gbe mailde.` f i eration.'

arrivesl 'through' v the connections leading"tov the lower.l v

half; the ig'grpasses' into tlieother'condition of: equi-rv lilariurn` and is then assumed'to` act upon-"the outgoing" @sessions ssnn'sstsd to .the lwerf half.:l .Return with@ 1'6" c'c'anditionL of equilibrium referred'to takes pla'ceonapplya Ther condenser "9i closes ,thecir'eq g 513i] Befsprearrsssdmge A various drawing; sqm

ends.

tion 41 to a trigger 42 which corresponds to a given con-A 7 ing a trigger 'pulse through one' of the connections .leading to the upper half of the rectangle. v

Af gate circuitv represented by a circle to which lead two ingoing connections and from which a number of connections may leave. -There is a signal on the outgoing connections only when there is, at the same time, an effective signal on the two ingoing connections. lAccording to the nature of the ingoing signals, the signal obtained on the outgoing connection or connections may be the part that is common to two pulses or anoutput alternating signal available during the time in which the control connectioniis transmitting an effective signal. A square which comprises within it the symbol of a rectifier, represents a detector.,` This may, according to the case, bea detector tuned: to va given frequency or av pulse-detector for amplifying pulses and regenerating the wave `form thereof, if distorted, in order to produce well 4calibrated .pulses for the triggering of triggering circuits. 1

The nature ofthe other rectangles represented in the gure is explained in the text or in other figures. They are,'in general, devices which belong to the calculating partl of the central office and which'will not bedescribed indetail herein.

Referring to Fig. 3, the equipment of one of the ten trunk lines that are connected to the concentrator comprises a transformer 30 having four windings. The primary winding 311 is connected to the trunk line 15 and its middle point 31 -is tapped. One of the secondary windings 312 is connected, through a power amplifier 32, to a pulse-generator 33 which forms part of the inside of the central oice. The function of this generator is to transmit, under the control of the central office, the positive disconnecting pulses which produce the release of the crosspoints both on the concentrator side and the side of the internal-selection stages.

Another winding 313 of the transformer 3i) is connecting pulses to the points such as 37 and positive two-` sided connecting pulses to the points -such as 38.

The rectangle 39- represents the part of the central office for markingl a particular concentrator, i.e. the concentrator in which a called subscriber is to be found, and.

for producing, in the time interval characteristic of this subscriber, in his concentrator, the transmission ofnegative two-sided connecting pulses which will have the effect of producing, in synchronism with the positive two-sidedy connecting pulse transmitted Vat that instant through the subscriber-fs gate in its idle condition,vthe operation of one of the crosspoints associated with. the line of the called subscriber. The negative pulses transmitted by the gen erator39; are appliedthrough. resistors such as 40 to the taps 31 of the primary windings oftheten trunk lines of the concentrator but they could be effective only on those which have not already'been connected at their `In addition, they Vare transmitted by the conneccentrator and is common to the te'n trunk circuits such as 29 connected to said concentrator. The function of this trigger 42 is to keep the memory of the fact that a two-sided connecting pulse-has just been transmitted by' The junctor 43, which is located between the group ofv three internal-selection stages 34 to which itis connected Aby the transformer 44:'and 'the symmetrical group to whichit is connected by the transformer 45, comprises, in addition totestingcrc'uits (not shown, because they take .part only in the internal operationof the central olce), a band-stop lter 46 `which prevents the loop frequencies transmitted by the gates of the subscribers from being propagated outside the half of the central oice which interests them. These frequencies, which, in fact, serve for the supervision of the condition of the subscribersloops, should not be mixed.

Thedetection and signalling transmission devices associated with the trunk-line circuit 29 will now be described.

p When one of the crosspoints 13 cornes into operation in the concentrator, it'produces the passage of a current;

of a few milliamperes in the connection leads 11 and12 inv series,then asharp rise in the potential at the'terminals of the resistor 16 of Fig. 2. The condenser 47 transmits this rise in potential inthefform of a positive connectioncontrol pulse to the two wiresV of the trunk line 15 in parallel and this positive pulse, which is picked up; at the. tap 31,-' crossesthe diode 48,and leads to the pulse-detector 49 which, kafter having regenerated it, uses lit to trigger the trigger-circuit 50. Vin Vits operated condition, this trigger circuit opens the gates 51 and 52 f in order subsequently to allow a pulse 104, coming from a common generator 8B, to pass. The pulse 105, which, at this moment, leaves the gates 52, is applied, on the one hand,.'to a scanning circuit 54 through the lead 81y (circuit 54l will be describedhereinafter) and, on the other hand, resets the trigger Acircuit 50 to its condition of rest, then closing the gates 51 and 52, The pulse (also which, at this moment, leaves the gate 51,y

has a number of functions, one of which is to restore to rest the common memory trigger '42 in the case in which the said trigger-had originally been put into operation by the transmission of a two-sided connecting pulse -by the generator 39. l Y

When a signal having the loopnfrequency f and ycoming from gate 3 of the subscriber connected to trunk 15 arrives at the transformer 30, it is detected by detector 55 which is tuned to the said loop frequency and which converts it into a direct current potential applied to lead 56.` Y Y The two trigger circuits `57 `and 58 control respectively the gates 59 and 60, to allow the passage of the dial tone frequency signal FN produced by the common generator 61 and of the ringing frequency signal F and ringing supervisory frequency signal F both produced by the common generator 62.

Trigger circuit 57 is operated when the pulse 104,

which is produced by the generator 88 on the wire 53, passes through the gate in consequence of the presence of a pulse v103 at the output of the trigger circuit 50,

that is to say, at the time when the crosspoint 13 is,V

operated and connects a calling-subscriber line. It is reset to its condition of rest when a direct current potential appears on the lead56 in consequence of the detection of the signal having the loop frequency, that is to say when the first dialling pulsefrom the calling subl Device 63, which comprises a differentiating circuit Vand a rectifier circuit, has the function of detecting the end of reception of the signal having the loop frequency. The differentiating circuit, which receives the direct current potential through the lead 56, gives, for example, a positive fine pulse at the commencement of the detection of the signal having the loop frequency and a negative fine pulse-'at the end;y Ithe rectifier circuit eliminatesthe',

Vsubscriber lifts hisl han Y the junctorf 43-and na 'second-selectorv stage-` shown t'o the trunk` line" circuit 297i connectedito the,calling positive? pulse andi allowsr'. vonly; Ytheendi negative. pulse to pass. l "v1 theznextgate 78for the'next positivepul'se ''liesstate y Trigger circuit 58 is operated thepulse y10`5which i leaves the gate 51,-thatzisltotsayl atth v vme Whencross-J point 13 is operated; .conditiontha gatelbefopen;

` r that isto ls arycvvhesrrfuiggergeirqrit*giis.operatedlbecauseV the line connected Vis aA called-subscriber line.fr Thus t nectiovn;V

ringing supervise'ry--frequen 'cy'v 1F Yanuninterrupted c frequency(havingnosilntrand ringingfsuccessiveinterl; Vval'sjtravels from; the trunk 'line'circuit 29fconnected lilez'th'e detectorfj'onverts ititintorfa 'direct current" Y potentialr on-the-wire 66.-* ,If-f trigger circuitfSSisat rest, which happens *irr they ca'se of `the"A trunk line'circui connected-to the calling-subscriber, the gate i'transrnits this uninterrupted signal to the circtiittt Whiheisjquite similar ltol thecircuit163. Consequently; Whentlle called subscriber vreplies, the transmission' of'- the Y" freqll'encyTF1y byfthe trigger: circuiti` Sf ofY the' trunlgl line ,circuit-1 whichl is; connected to` him being'fstopped'the-`end ofthedetec#y vtol the calling subscriber W'il'lproducre2 onjthewirejg;

thel transmission of a' pul'sefwhicli Will bei .usedy by cip.

cuits (not shown) vtfhiychvinterest'J only the 'central oiice'- forA any'us'eful purpose,` especiallyfforcharging the caller.'

"reset toerest: bye-thee pulse'- which;

' of the'signal'thavingjthe;loop t the 'time` Whenethel'ealledf t stopping'f j the transfr gesegnet of ,the ring vof trigger circuits is: then,1 thes'an'e'as beforefshifted one rowtowards the right andtheY con-k nection on which thetcontrolling pulse is'= found is no longer 3i9"butrr thenext'one 179'; The pulses are distributed successively-.over all'theiconnections' suchas 19 in synchronismfwith'therhythmic; operation ofthe pulse generator ZSfin the central oiiice. lWhe'n the-last't'rigger Vcircuit of .thersuccession is, in' the-positionof operation; vanegative pulseil isrLnormal1y{received, theetfect'ofY .Whichfis to ensure the resetting to vrestj-of allfth'e trigger circuits with the Yexception oftA the rstthe trigger circuit 71Whichvis reset in 'thefpositionlfooperation, thus Vde# j noting tvhesubscriber No'. 00`of` the iiftyt Eig-5 represents lt'he yprinciple oflthe scanning device' 54 which, ashas berenvseenreceives-from'the gate -52,.A n throughthe wire 81T, a: ne'3.connectioncontrol pulse1'05 when vrthe trigger circuit 50i is infoper'a'tion asthe result ofrthering of the lcrosspoint:lassociated with the con- 'centratortrunk-15.- 's I VThe-time interval in which''theconnection-control pulse in vwhich thel trigger circuit'50V is put into operation is chieti-y characteristic ofthe numberf ofthe'subscriber connected in the concentrator considered, `the -phase ofi ,the synchronizing pulses 101 Y of this stage being chosen so that one is assured that the loperation of .trigger circuit.v

59S t lastsfat least-.5; upv to"` the time 'of occurrence ofthe pulse 104v relating-to thennmberr of the concentrator tion'lofthis frequency in the 'trunk' linecircuitconnected' considered. Itfisrtorbe borne iny mind thatV it is Athe pulse 104- thatresets the trigger 50 and consequentl;I

the output pulse of trigger 50 ends at 103'. The pulse ,165 passingr'through the vgate 51 .andV'SZ isreallyzchar- "Thedirect-'current potential applied by the detector 55 Y to the wire 56 is also sent, through wireilgandgate 79',

to atscanning device 7 4 which'will befiiri'eflyjdescriljedf s hereinafter. lThis' gate 70 is open {1t/hen the triggerlcircuit S8`-isy at rest, in other Words lduringthe openingjofthe. loop due to dialling and or'when a Ycallingor` a called:

subscriber hangs up at-the endof' the communication,

Fig. 4 represents"the'principle of the operation ofithe pulse generator 18 relating/to the fifth concentrator.. It is'constitutedbya seriesoi` lifty trigger circuits 71,72, 73g etc., eachvof them supplying"subscriber-identifying pulsesy 1Min the appropriate time intervalsto the `Wires lsuchl as `19 in the directionn of'the'transformers 5: ando` of*- thesubscribersigates'. vIn Fig. l, the pulse 102`of theline c relatesfto"subscriber'No. 02'@ itisseenfthat.

it does not coincide .witlrthe time reserved@ fornsubscribier No. 02` (time niark'edfsubscriber' No;j02, on line a). This non-coincidence*takes*y place inorder to take into accountthetime' of propagation offthe con#v` and the delay; of operation of the nect'ion-control pulse c rosspoints. The synchronizing samefpolarity 'forV example; v`positive;'and of `e transformer" 2 7 by'; a Vdirectilflal couplingdevicef80`co'mposediof diodes' for directingthe positive p'ul's'e'sA tothe step-by-step trigger Lconnec- 'ttionf75fand thenegativel'pulses to the'resetconnection 76. Ifl it Ais assumed, in the iirst place,1tha't onlyv theA trigger circuit l71 corresponding to the :r'st'subscribe is in operae pulses 'offa' recurrent cyclle'are' comf. vp'osed'of a train'of fortynine fine" pulses' 1011` of'thefv t negativeo pulse 9101` for ensuring'theresetting` of" the trigger circuit '".ringtofthe initialfpositipngof,the cycle. 'Ih'leyare Yref t ceivedlat the output off tion; a positive pulse isthen found'on the connection 191 of-thisisubscriber and thegat'e 77 isjope'n. "Ifhe rst positive pulse 101 receivedrthroughwire{75,and passingthrough gate 77, which isfthe onlyone that' is open,` puts the next, trigger circuift'l72v into operation;

theleiect'of this is to' produce,' a very shortiristantafter,y

the' resetting tork rest" of trigger circuit-71 and unblockiiig acteristic both of.' thenumbe'rV ofthe subscriberv andlof the'number of the concentrator considered among they I hundred (concentrator'No.vv 5 in the' case of Fig. 1). The

ypulse 105, which is propagated on thewire 81 therefore characterizes, entirely by lits timeinterval, the numbervr 10i!- thei subscriber among the ve'thousands who hasr just been connected. There remains: to be' known, `in` I orderY to define entirelythe' connection made, the Yconcenfy trator trunk-line Anumber inv theconcentratorwhich iis being used for the communication.l The scanning device, Y

which supplies this indication to the internal central office, comprises, on the one hand, the set of a thousandgates such 'as 52v which have been'collected in Fig. Y5 into a' ofthe generator-88; islto openy successively the gates 52.v t Vofthe concentrators. At a'l given instant, no pulses .can t ybf,-four1d on more.. than onev o f the. tenigat'es l52""v'iihich aref connectedftoa Wire" 53, si 'gefasfthe instant Y question isl cated in a'major cycle rlat g tothe fum]- ber ffa particular subscriber; i that sub, A connected only -Withga single ione; of the tenv concentrtor' trunk circuits29`off his concentrator; "In-thesame'wayi pulses' cannot be Yfound onA morethn one" of a hundreds gates 52AWliichare con'recterl-y toa wire-z81lsinceeachy i relates'toa differentilconcentratori- Consequently; only;

a single? output. pulsel can: be'. foundfl at atim'eon onejo'f:

theztenwiressuch as .81; Eachfrofftheftenvwiresy 8111 isf characteristic` ofj thetrunk-circuitxnumben' in; thefconcentrator used.

The connectoncontrol g pulseeof;` the subscriber NQ- i' is represented atriv103 and. the corresponding lnilse'gatthev output ofthetriggergcircuit' 50,'fis representedat 1,93? int FigQ l, line d.

.-I*he identification pulses of a given 'concentrator, concentrator No. 5, are represented at 104 in Fig. 1, line e.

The` ne connection control pulse of subscriber No. 02 in concentrator No. 5 is represented at 105 in Fig. l, line f,

lf the connection control pulse 103 arrives through the lead S2 corresponding `to the second trunk line of concentrator No. 45, onlythe gateV marked 52 in Fig. 5 will become operiattheV instant of coincidence of the signal 103 andthe pulsev 104, and a :une pulse 10S for controlling the connection will be obtained on the wire marked- 81cm Fig. 5 (second wire fromfthe top) which characterizesthe secondtrunk line.-

The diode decodery54 distributes the pulse 105 that arrives on one wire among ten over one or more of four wires which lead to the triggerlcircuits S4 to S7, formingV the counter 109. The cabling ofthe diodes is effected in such a mannerthat the position taken bythe four trigger circuits 84 to S7 represents, in a binary code for example, the number of the concentrator trunk line in the concentrator used. In the Vexample described, the trigger circuit 86 comes into operation; this denotes the second concentrator trunk line.

Theseven triggers 111 to 117 of generator 88 form a binary counter'118,?allowing the number of the concentrator used which is comprised between 1 and 100 to be translated into .bina1y numeration. Y

A third binary counter 119 comprising six' triggers 121 to 126 and controlled Aby the resetting pulses of the counter 118-allows the number ofthe subscriber (comprised betweenO() and 49) to be translated into binary numeration. 1

The instantaneous information, supplied by the counters 109, 118 and 119, supplies all the necessary information to the central oice switching network in i transformersS and 6.x For order to -know the number of the subscriber, the number of the concentrator; and the number of the trunk line relating to said concentrator which have just been connected. The detailed description of the employment of this information by the electronic central oihce is not within theA scope of the present invention.

The device 74 for scanning the condition of the loops of the subscribers lines represented in Fig. 6 has a constitutionzwhich is verysimilar to that of the scanning device comprising the matrix 83 and the decoder 54. It comprises essentially a rectangular switching arrangement 741 of a thousand ,gates such as 89, each receiving one of the wires such as 90 coming from the gates 70 of the trunk-line circuits 29 and, through a connection such as 53, identification pulses of the concentrators.

The signalling transmitted over the connections such as 90 signify that the subscriber is effecting loop breakages with his dial or that he has just hung up.

It is necessary forthe central oce to analyse, at particular instants, ltheV conditionof the loop of every subscriber so as to be able to deduce the numbers formed on the dial. In order to know the location of the ten subscribers who may be connected to the central oice by the same concentrator, it is sul'licient to cause the generator 92 totransinit a pulse 104 to the wire 53,v corresponding to this concentrator in order to collect, kover the'set of ten wires `93, pulses which characterize the state of the corresponding subscribers; thisv information will be used by the central olce for makingV the connection.

Beforeproceeding to the detailed description of the operationof the concentrator, it will be shown that the gates 3 of the subscribers, which are assumed to be constituted by saturable-core transformers, arev quite capable ofataking four distinct states referred to in connec-v tion with Fig. 7.

Fig. 7 represents the points of operation on an ampere-turns of energization-induction diagram,gwhich are used in the four states for each of the saturablefcore 12 each of these statesl or service conditions which will be called respectively:

Idle or line disengaged, Loop closed, not connected or calling line,

VLoop closed, connected or line in use,

Loop open, connected (dialling or hanging-up),

the two hysteresis cycles of the transformers `5 and'6 have been represented by plotting, in abscissas, the excitation ampere-turns and, in ordinates, the induction. The

black point represents, on each of these diagrams, the

polarization point in each state in theV absence of subscriber-identifying pulses 102 on the lead 19. -The thick a weak direct current, which passes through thev cou-y nection 19 to a resistor and a negative source in the pulse generator 18,- is such that the cycle described during the subscriber-identifying pulse remains, for the transformer v5,V in the region of saturation and therefore does not give rise to anysignal but enables the transformer 6 to describe `a hysteresisV cycle, thus supplying the positive two-sided connecting pulse 106 to the lead 11 (Fig. 7, line a). Y l n p When the subscriber liftshis handset and closes hisV loop, the microphone-feed current which passes through the primary windings of the transformer 5, displaces the normal polarization point to the right, whilst nothing is changed for the transformer 6. At the instant at which the pulse is produced on the lead 19, the polarizations are such that the two transformers describe simultaneously a hysteresis cycle, thus uspplying to the connection 11 a one-sided connecting pulse 107 of an amplitude which is about double than that of the two-sided connecting pulse (Fig. 7, line b).

After the firing of the crosspoint 13 (connected closed loop), a direct feeding current passes'through the leads 11 and 12 as well as through the secondaries of the transformersS and 6 in series. The polarization points are then both displaced to the right in the second region of saturation and the pulses that arrive through the lead 19 no longer have any effect (Fig. 7, line d).

W'ten the subscribers loop is opened, for example by the breakage of his dial or because the called subscriber has not yet lifted up his handset, andthe line is con nected in the concentrator, the interruption of the microphone-feed current which results therefrom reduces the energization ampere turns of the transformer 5 without influencing those of the transformer 6. As the polarization point of the transformer 5 is, at that instant, i'n the vicinity of the saturation knee of the hysteresis curve, the pulses are practically without action, whilst, on the contrary, the signal having thek loop frequency f yinjected into the fourth winding of the transformer, has an amplitude which `is sufficient for producing variations of mduction which are found on the lead 11. The subscrlbersjgate 3 therefore allows the signal having the loop frequency f to pass only in thisl case (Fig-7, line c).

lt will also be assumed herethat the crosspoints used possess the known properties of cold-cathode gas diodes,

namely that they can be made conductive by means of f Ya pulse Vthe amphtudeof whichvexceedscertain threshold value and are blocked by means of a pulse having its amplitude 1n theopposite direction and of asucient duration, and also that, when a plurality of diodes, which possess a common load impedance, are simultaneously.

energized, only one of these diodes can Vbe kept in the i red condition. i

.The detailed operation in the case of a start-ing communication is then as follows:

When the/subscriber 1, on lifting his handset, loops the line 2 to the impedance of his telephone set, the gate,

i currentfpa'ssing through one. of ythe -zdeliversg; to the lead: 1:11,"a one-sided?1` connecting pulseV 107 yat the instant: atiwhichfit receives' from. the: genera tor 18, over the connection 19 the Vsubs,criber-identifyingv pulse-.@1021- at the timeinterval thatfis: charac'zteristicv of A y.the number off the Ysubscriber in the concentrator.-

' The amplitude oflthis pulseexceeds theztiring. threshold valuecfathe gas diodes'- 13 whichsare connected'to anl availabletrunk: line-15, 'thatf isto sayl to: a' common resistor: 16 wh`ich1 has :not already` been1 traversed byl at feed tothe trunk line considered; L

These gas diodes which have a common load impedance ,thatfis :constituted by the resistance'fl'," block one another and;` onlyeone'of `themcan pass tol theV completely *conductive condition.

fifty.I diodes connected t On tiring', the diode 13Lproduces Va When thecentral o'iceldecidesthat the' number; dialed",

on the dial has been receivedv completely and ,that it` ha's the necessary .elements for making the-connection, it

proceeds to' the.. connection'V ofthe called subscriber through a trunk line of the concentrator ofthat'calledf Y subscriber, as willzbe'seen hereinafter; then,h'avinglrecog nized the-.number of the; trunk line chosen/on thecalled sliarplincrease of"voltage at the upper terminali ofthe-V common'4 resistor- 16,: thus rendering Vthe corresponding ti'unk1line unavailablefory "otherf connections. Vlrl`=his Vincreaseiof/voltage, vWhichaisdiiferentiatedlby theconde'nser f- 417,.is. transmitted,v in the formfof 'a connection-controlVV pulse 103, to the-tap of the transformer 1'4` andgfin parall lel, to the two-Wires 15 of the trunk lineup tothe tap 31.- n

A-ften'having passed throughttherectifyingdiode 48, this pulse is detected andv regeneratedV by. the' pul'sedetector 49zand; finally, triggers the triggercircuitlSU` The phase*y side, it proceeds to the connection-of` the' tWogro'ups 34; Vof thefrinternal selectionlstagesbyrmeans ovfj'the"marking4l and' connecting devic`e536, the detailed"description/ofi which is outside -therscope of this inventiorn?` The calling 'l subscriber 'can th'en. perceive, through circuitj29 of: the called Side.'v t thesametimeQitswn Ytrunkline circuit detects'fbymeans ofithel'tuned detectorv f 65, the return-offcall :supervision rfrequency andi-transf v mits ittto the .devicefS'A through the gate 61' lerlfsincev the `,trigger circuit 581' is atrest.i t Y n VWhen thecall-return signal at the frequencyiF stops' owing to'liftingof his handset' by the called subscriber,l

thefdevicef'z68"transmitsr to* the connectionY 69 a pulse n which will be called reply pulsei andwhich is used by` Y 7 thescentral oflice fory all usefulpurposes," especially forY displacement between therhythmrof thelcentralioice t.

andithe subscriber-identifying pulses: from the generator 18,1 taking. into account: the'.y propagation times;l onlth'e` one::hand,z 'and the .mean-"timesofi starting! vthe gas :diodes Y 13; onthei other hand, should-be such that 'the triggering off/the' trigger circuitr50 is produced slightly before the nglinorf;'cyclefofrthe concentr'atorl whichfforms'-5part' off l tiret-major cycleA of; the subscriberrfconsidered ibut after thefsametminor'cycle Whi'chyformsfpart'of the preceding major'lcycle.; ".Thel adjustment:v margin, .which is thus slightly'lessthan'two milliseconds, is verylwide for elec-v tronidevices.;` 'Infparticulan it enables fthecentral-oiiiceA torba-prepared` for'the recordingv of the' identity of the calling: subscriber andthe trunk line ofr his connecting eoncentratorr, The details of' thesempreliminary operationst-areoutside the scone'ofi the present invention.

When afminor cycle that is characteristic of'the con- -centrator'is arrived' at, the pulse-generator 88 supplies a l concentratoreidentifying pulse 10410 the wire 53. This pulsezp'asses through the. gatesv'l and 52"which are open anditproduces three: eiects: it startsfthe trigger circuit 57 which opens the gate-59 'to the frequency FN of'the dial t0ne,vwhich tone isv receivedtby the calling subscriber; itrpassestothe wire 81i and'throug'hvthe diodedecoder 54,=tputs one or more trigger circuitsr84 to 87 into opsi'gnalling thecommencement of the period of communi= cation tobe charged for, effecting the metering of effec- Y' Y tive tratiic etc. n e i n v y The'retransrnission of the supervision of the reply from the called s'ubscriber'is'` interesting for a nu'rnbervof reaf i sons and especially forenabling thelpricing operations@ tolbeg chargedY to the' calling subscriber `Vwithout'. necessitating: a memorizingA of'lthe communication'established" hetwe'enlth'e twozsubscribersj and also' in the casein-which thet-ingoingline is constituted" by an.- interurban circuitfor: 'eas/ilyretransmitting. lthe supervision to tlflecall oiee whichi'musticarry. outrthesev pricing operations. f

f L When,the"sub`scriber1hangswup at the end ofthe com# munication, the breakage fhis loop produces ythe same I 'succcssion'of phenomenaaas during the breakage by thel dial, andthey centraloffice makes use, inthe same way,V

ofathesmeans forE testing the ,hanging-up; It distinguishes a'Ihanging-.upfrom a dialfpulse by ascertaining that the direct'potential' onlead 90 lhas ay durationthat is'greaterf i thani200irnilliseconds for example, byfmeans offa delay device which yis not described/here. Y

rWlzlenthe'central oice, onrtestin'g the presence ofi int formation oflrsucient duration/on; the connection 90',

eration so'as to record on=the1counter1091the number of: thectr-unk line oftheconcentrator. which'l hasbeenl -uscdfor ensuring the connection and, iinally," itiresets thezvtrigger circuit-50torest;.the eiectl of this` is torecloseithe gatesS'l andfSZ; Whenjthe subscriber operates his dial; everybreakage"` of the'loop', onfchanging'fthe n po'intof'polarization` of the-V transformer-f5, allows the t passage ofthe loop frequency. f through theffdicdej13,

transformer: 14: and the trunk line `1.5. This'rloopfre-f quency; which is -pi'cked `upI by "the, secondary winding 3137.1of thetransformer 30,v is detectediby thedetector slintolfa-'direct'currentpotential onfthe lead :56. The commencementoftherfirst' dialling pulse received resets;Y thef trigger: circuit 51'tojrest and s stopsI thextransmission offthefdalztone"by-closingfthe gate 59.'

ascertains 'thatthe subscriber has hung up 'and *decidesl to cut himiot, it transmits, by means ofi the pulsegenerator133,to theV particular connection which leads to the amplifier 3250i the trunk-line circuit considered, a'pos- Y itive disconnectionpulse, the amplitude and the duration yoflwhich':arevsuiiicientwfor producing the extinction of the'crosspointus'ed through' the intermediary ofthe trunk linexlandfofthe trar'rsforrner'14, and also kof the cross'- pointsxbelou'ging'to three internal selection stages'34`up' tothe: jnnctor'43throughthe intermediary'V of the trans, f-

A for'nier 30.` 1

e n 'This:disconnection'pulsey hasv` no 'effecting vthe tap 31 of the transformer` 30 rand, Aconsequently,there isffnof.V r-isk=1;off producing ajfalse signal-cnthe detectorf49.v A'

`1t/rest; thefdir'ect'current' potential is carried 'tothejcon-r` nection''90 andis, consequently,` availableferr being analyzed.' by the centrali'ofiicet by meansoftthe 'scanning devic'e 74'lati the `time that ispsitabley for it Forfthis purlriose,y itis 'sutircient forl it totra`ns'mit,tby meansiof-the pulse-generator 92, av pulse1`torthe ulead, 53 rthat.'coire`Vr sponds :toV the. 'concentratonz linl order tof tnd,:on1thel lead informationA` that. is" necessary toi '.93': corresponding tol the number ofthe-trun1 lill??? the l te municatonis as i follows: 'f

. The detailed operation' in the case of an arriving comsidedrconnecting pulse.y This pulsey has' 'twolv objects;l itlputs; into operation'the memory trigger circuit 42 which iskassociatedlwith the concentrator equipment 1in thef`cen traf otlicer andthe object of to recall' thatfthe I5 connection control pulse, which one is prepared to detect, relates to a called subscriber; it is then, through the resistors 40, distributed to all the taps 31 of the trunkline circuits, flows in parallel on the two wires 15 of the trunk lines and through the condenser 47 and then appears at the terminals of the resistors 16.

As at this precise instant, the gate 3 of the called subscriber is delivering a two-sided positive connecting pulse to'the lead l1, it is seen that all the diodes 13, which correspondY to available trunk lines, find, at their terminals, a difference `of potential which is the sum of the amplitudes of the two two-sided connecting pulses of opposite polarities and, consequently, exceeds their firingl threshold.

However, as all'these diodeshave a' common load impedance,v constituted by the resistor 17, only one can fire while the others remain extinguished. The diode 13 which isconductive discharges into the resistors 17 and 16, thus marking the busy condition of the corresponding called line andtrunk line. It also produces a sharpl increase of potential at `the upper terminal of the resistor 16 which, having been differentiated .by the condenser 47 and retransmitted in parallel by the two wiresV 15,.is detected Vby the pulse detector 49 in the same way as during the connection of a calling line to an available trunk line. The same operations of identifying the trunk line chosen take placeand the central office can thus know the incoming trunk line and the outgoing trunk line to be connected together. It proceeds to the connection as has hereinbefore been seen.

However, the effects'of the operation of the trigger` circuit 50 at the interior of the trunkA line circuit are somewhat different from the case of the connectionof a calling line. The pulse S transmitted by the gate 51 cannot put the trigger circuit 57 into operation be` cause the latter is kept in the position of rest by the direct current potential which is found on the connection 56 as the result of the detection of the loop frequency by the detector 5S (because the called subscriberloop is open). On the other hand, this pulse passes through the gate '64 `which hasbeen opened vby the memory trigger circuit 42 and puts the trigger circuit 58 into operation; at the same time, it produces the resetting of the trigger circuit 42 to rest and, a very short instant later, the closing of the gate 64.

In its position of operation, the trigger circuit 58 opens the gate 60 to the passage of the cadenced call frequency F and of the continuous call-return supervision freherein'before been seen, his trunk line circuit kdetects the call-return supervision rectified frequencyl.Y which is not Iaudible but isalso propagated through theint'ernal stages of the central station. v When the called subscriber lifts his handset, he ,prof duces a modification of the' characteristics of his. gate 3 which, as has hereinbefore been described, issuch that all transmission of signallings lby the line isv stopped.

- The stoppage ofthe detection of the loop frequency therefore produces the elimination of therectied voltage put on the wire vSe by the detector 55, and this` interruption is translated by the device 63 into the form of a pulse which resets the trigger circuit58 to rest,

closing the gate 6@ and consequently stopping the transmission of the frequencies F and F..

Since, during the transmission of the frequency 13",. the detector 65 of the same trunk line circuit put a4 rectified voltage on the wire 66, the precaution should be taken notto open the'gate67 too soon after having yto closed the gate Y at the instant of the triggering of- 58. For this purpose, a slight delay is produced in the opening of the gate v67.

During the timeof the communication, all the devicesl Yused arein the condition `of rest, with :the exception ofk the crosspointsofthe calling and called subscribersvlines with the selected trunk-lines and the crosspoints in use in the internal Vselection stages of the `central station.

The,u freeing of the portionof chain located between' the called subscribers line'and the junctor 43 when thesubscriber replaces his handset is produced'asv has here--` in-before been indicated.

' The concentrator, which operates in connection with anpelectronic central office and. forms the .subject matteri of the presentinvention, has been described in the pres-- ent specification in the form of a well-defined embodiment. .However, it is to be understood that numerous modifications are possible, especially in the choice of' l. A telephonie concentrator arrangement for allow-Y ing la number of telephone subscribers lines to be con-V nected to a central station by a smaller number of trunk lines comprising a matrix of crosspoints having as many input 'leads as subscribers lines connected to the con-` centrator and as many outgoing leads as trunk lines between the concentrator, and the central station, a plurality of subscribers gates, each relating to a given subscribers line and being formedV of at least two saturable core transformers in series located between and coupling said given subscribersline and the corresponding input lead of the matrix of crosspoints, a subscriber identification pulse distributor having a number of outputs equal to the number of subscribers and ...producing on said outputs pulses the time-intervals of which in a recurrent cycle are characteristic of the numbers of the subscribers, connecting means between said pulse distributor outputs and said subscribers gates, a signalling frequency generator vand connecting means between said signalling frequencygenerator and said subscribersgates.

2. A telephonie concentratorarrangement forv allowing a number of telephone subscribers lines to be connected to a central station by a smaller number of trunk lines comprising a matrix of crosspoints having as many input leads as subscribers lines connected to the concentrator and as many outgoing leads as trunk lines between the concentrator and the central station, a plurality of subscribers gates each relating to a given subscribers line and beingy formed of a first transformer,

former in series, a subscriber identificationV pulse dis-,.

tributor having a number of outputs equalto the number of subscribers each output being connected to the primary winding ofthe thirdxtransformer in series .with

the second primary .winding of the second transformer of a subscribers gate said distributor producing onV said outputs identification pulses the time-intervals of which in a recurrent cycle are characteristic Vof the numbers .of the subscribers, a signalling frequency generator having an output connected to the third primary winding 0f said second transformer, the rsaid input leads of said matrix of crosspoints being respectively connected to the secondary Winding of the first, second and third transf formers Ain series the subscribers gates, thesaturation of thesecond and third transformers of a' given Vsul:- scribers gate being thus responsive to the operation of acrosspoint connected to said subscribers gate through the corresponding input'lead, and the said outgoing leadsfof said matrix being connected to the trunk lines whereby the subscribers gate is adapted to occupy four distinct states according to the service condition of the subscribers line, namely a iirst state corresponding to a v subscribers handset on hooi;V and a line n ot connected to the crosspoint matrix in which the second transformer is unoperative and the third transformer unsaturated and the subscribers identiication pulse gives rise through thergate to a small amplitude pulse, a second state corresponding to a subscribers handset olf hookrand a line disconnected from Athe crosspoint matrix in which the and operative and the subscribe1"sidentiicationV pulse esauritay is second and third transformers are Vboth unsaturated Y 2724746 corresponding to a subscribers handset on hook and a line connected to the crosspoint matrix in which the second transformerwis almost saturated and the third 10 transformer quite saturated and the signalling frequency gives rise toa characteristic open loop signal.

References Cited in the tile of this patent l UNITEDVVSTATES' PATENTS Bruce et al. ---a Nov. 22, 1955 2,812,385 Joel et a1. Nov. 5,-1957 

